Field of the Invention
The present invention relates to methods for visualization of heart scar tissue.
Description of the Prior Art
In certain therapeutic and diagnostic methods, such as for the implantation of cardiac resynchronization therapy (CRT) devices, information about heart scar tissue is essential for the placement of the left ventricular (LV) lead. This information should not only include the location, but also the transmurality of scar, as both affect the effectiveness of CRT. It is then necessary to attach one or more electrodes to the heart to enable measurement or monitoring. The electrodes should preferably not be attached to a region of the heart wall composed of scar tissue, although acceptable contact may be achieved even with scar tissue present, if that scar tissue is on the inner surface of the wall, rather than the outer surface, where the electrode is to be attached.
FIG. 1 shows a representation of a wall of a left ventricle of a heart in short-axis view as captured in MRI imaging, and FIG. 2 schematically illustrates the heart wall in Long Axis view: the myocardium 10, which extends between an outer surface 16, the epicardium, to an inner surface 18, the endocardium with regions 12 of scar tissue illustrated. Electrode 14 should preferably be attached to the external surface 16 of the heart wall 10 at a region where no scar tissue is present. It is also acceptable to attach an electrode to the external surface 16 of the heart wall 10 at a region where scar tissue is present on the outer surface, although scar tissue may be present nearer an internal surface 18 of the heart wall, such as in region 12a. Conversely, regions such as 12b, where scar tissue is present at the outer surface 16, but for a limited depth, may be used for attachment of an electrode.
It is thus important for a clinician to be able to know not only whether scar tissue is present at a part of the heart wall, but its depth and its position within the thickness of the wall. The depth and its position within the thickness of the wall may be referred to as the “transmurality”.
In one conventional method, late-gadolinium-enhanced (LGE) magnetic resonance imaging (MRI) is used to obtain pre-implant images that provide information about the location and transmurality of scar. However, the assessment is mostly manual, as tools for assessment are not yet widespread. In particular, the assessment of the transmurality is difficult and mostly performed by considering a short-axis view of the left ventricle obtained by MRI, see FIG. 1.
Some computer-implemented tools for assessment are known, and these focus only on simple representation of scar tissue distribution, for example the bull's-eye plot shown in FIG. 3. In FIG. 3, the bull's-eye plot represents an “unfolded” view of the myocardium around one heart chamber.
In this example, the myocardium is divided into sixteen regions 1-16. The region furthest from the apex is divided into six regions 1-6; the region nearer the apex is divided into a further six regions 7-12, while the region around the apex is divided into a further four regions 13-16. The shading applied on the bull's-eye plot of FIG. 3 represents regions of scar tissue. It is a projection of the scar in the myocardium to the epicardium. It is called scar distribution. Here, regions 6, 5, 11, 12 can be seen to comprise scar tissue over most of their respective surfaces. Most other wall regions show some scar tissue. Region 3 is shown as practically free of scar tissue, and may represent an acceptable site for attachment of an electrode, even though some scar tissue is present at, or near, the internal wall surface.
FIG. 4 represents some automated analysis of the bull's-eye plot of FIG. 3. Region 5 is shaded, since is it measured to comprise scar tissue over more than 50% of its surface, and so to be unsuitable for attachment of an electrode. The remaining regions each comprise scar tissue over less than 50% of their surface. This measurement may be known as “scar burden”.
FIG. 5 represents the results of a calculation of transmurality, based on the data of FIG. 3. Regions 4, 5, 6, 10, 11, 12 are shown shaded since the scar tissue in these regions extends to more than 25% of the wall thickness. Those regions may accordingly be deemed unsuitable for attachment of an electrode.
While the above bull's-eye plot type representation of FIGS. 3-5 provides some relevant information, it remains difficult for a clinician to interpret the results, as only coarse information is presented and there is no location of the position of the scar tissue within the thickness of the wall in any region.
The approaches mentioned before either rely heavily on manual interaction or provide only coarse information. The review of the segmentation in the 2-D short axis representation of FIG. 1 is cumbersome and time consuming for a physician as it is necessary to scroll through many slices of image data. The bull's-eye plot representations of FIGS. 3-5 provide only coarse information, which may be insufficient to perform a good assessment of the underlying condition of the patient.
JP2015029518A discloses a method and arrangement for displaying a representation of different tissue types, particularly imaging the head: where the tissue types essentially consist of skin, blood vessels beneath the skin, bone, blood vessels beneath the bone, and brain tissue.
JP2015029518A describes obtaining 3D image information regarding the location of tissue types (e.g. blood vessels) in lower layers (under the skin and under the bone), then representing features from those layers on the image of the upper layers, or actually projected onto the skin itself. The combined presentation of such imagery requires the layers to be made transparent.
JP2015029518A provides projection of all anatomical tissue types to one of these (i.e. the skin). This projection results in a 2D visualization of all the tissue types and overlapping parts are identifiable. JP2015029518A requires a transparent modelling of the different tissue types, that they can be distinguished in the 2D projection based visualization.